1. Field of the Invention
The present invention relates to a coupling for transferring torque between a torque input member and a torque output member. In particular, the present invention relates to a multi-directional coupling having a plurality of operating modes for selectively transferring torque between an input shaft and an output shaft.
2. Description of the Related Art
One-way clutches and couplings are widely used in the automotive industry, for instance with transfer cases and automotive accessories, for transferring torque between a driving shaft and a driven shaft and for allowing the driven shaft to over-run the driving shaft when the speed of rotation of the driven shaft exceeds the speed of rotation of the driving shaft. Examples of common one-way or overrunning clutches presently in use include sprag-type clutches, roller-ramp type clutches, and spiral-type one-way clutches.
The sprag-type clutch generally includes an outer race member, an inner race member, and a number of wedge-shaped xe2x80x9cspragxe2x80x9d elements disposed between the inner race member and the outer race member. The sprag elements are shaped so as to allow the race members to rotate or xe2x80x9cfreewheelxe2x80x9d relative to each other with a first relative direction of rotation, and to lock the race members together with a second relative direction of rotation. The roller-ramp type clutch is similar to the sprag-type clutch but includes a number of roller bearing elements in replacement of the sprag elements. Since both devices rely on a wedging action to lock up, the sprag elements, roller bearing elements, and the races are subjected to high radial and Hertzian stresses during lock up. Consequently, such one-way clutches are prone to failure.
Spiral-type one way clutches have been developed to overcome the deficiencies of the sprag-type and roller-ramp type one-way clutches. Conventional spiral-type one-way clutches include an outer member having an inner spiral race, an inner member having an outer spiral race congruent with the inner spiral race, and a number of elongate roller bearings disposed between the inner and outer races. The elongate roller bearings provide an even distribution of compression forces on the roller bearings and the races. However, conventional spiral-type one-way clutches typically only have a single mode of operation, namely, they lock up in one relative direction of rotation and freewheeling in the opposite relative direction of rotation. Further, the design of automotive equipment using such one-way clutches can be quite complicated.
Programmable couplings have been developed to provide a clutch with a number of operating modes. For example, the PCT publication WO 99/28645 to Kerr teaches a programmable multidirectional coupling which includes a tubular housing, a race associated with the housing, and tubular slipper disposed between the housing and the race. The slipper includes an inner friction surface for engagement with the race. The housing inner face and the slipper outer face together define a substantially cylindrical channel therebetween for receiving a full complement of roller bearing elements. The housing inner face also includes a number of cup-shaped recesses, and the slipper outer face includes a number of complementary cup-shaped recesses, with each opposing pair of recesses defining a pocket for receiving one of the roller elements therein. Additionally, the coupling includes an actuator for selectively uncoupling the slipper from the race for providing multiple modes of coupling between the race and the housing.
However, since coupling lock-up occurs with high pressure sliding between the slipper and the race, cold welding can occur between the slipper and the race. Further, the slipper inhibits oil flow between each roller element, and between the slipper and the race. Also, to ensure that the strut angle of the coupling is sufficient to allow the coupling to lock-up, the side walls of each cup-shaped recess must be manufactured with a shallow incline angle, thereby limiting the working depth of the recesses. Consequently, the roller bearing elements can leave their respective pockets, leading to early clutch failure.
Therefore, there remains a need for a coupling which offers a plurality of coupling modes, provides an even distribution of compression forces on the roller bearings and the races, and is not prone to cold welding or bearing misalignment.
According to one aspect of the invention, there is provided a multi-directional coupling which addresses deficiencies of the prior art couplings.
The multi-directional coupling, according to one embodiment of the present invention, includes a housing incorporating a first bearing surface, a race including a second bearing surface opposite the first bearing surface, a plurality of roller elements, and an alignment cage. The first bearing surface and the second bearing surface together define a channel therebetween for receiving the roller elements. The first bearing surface includes at least one recessed bearing surface portion which is configured for receiving one of the roller elements therein for coupling the housing with the race as the one roller element moves relative to the housing. The alignment cage is disposed within the channel for controlling the spacing between the roller elements. Preferably, the multi-directional coupling also includes a mode controller coupled to the alignment cage for controlling the relative movement of the one roller element and thereby alter the coupling mode of the coupling.
According to another embodiment of the invention, there is provided a transfer case which includes a torque input shaft, a first torque output shaft coupled to the torque input shaft, a second torque output shaft, and the multi-directional coupling for transferring torque between the torque input shaft and the torque output shaft. The coupling housing is coupled to the torque input shaft, and the race is coupled to the second torque output shaft. Preferably, the transfer case also includes a mode controller coupled to the alignment cage for controlling the relative movement of the one roller element and thereby vary the torque transfer between the torque input shaft and the second torque output shaft.